When a radio base station sends downlink data, the radio base station sends information regarding assignment of a radio resource used for sending the downlink data and downlink scheduling information, such as a transmission format, to a mobile station which is the destination of the downlink data via a PDCCH (Physical Downlink Control Channel). The radio base station performs coding and modulation of the downlink data, mapping of the downlink data to the radio resource, and the like in accordance with the designated downlink scheduling information and sends the downlink data via a PDSCH (Physical Downlink Shared Channel). The mobile station determines whether a PDCCH the destination of which is the mobile station is included in (candidate) PDCCHs. If the mobile station detects a PDCCH the destination of which is the mobile station, then the mobile station decodes the PDCCH and receives the PDSCH and the downlink data on the basis of the downlink scheduling information included in the PDCCH.
FIG. 26 illustrates PDCCHs and PDSCHs. A 1-millisecond subframe is illustrated in FIG. 26. In FIG. 26, a vertical direction indicates a frequency and a horizontal direction indicates time.
As illustrated in FIG. 26, physical downlink control channels (PDCCHs) i, j, and k and physical downlink shared channels (PDSCHs) i, j, and k are assigned to frequency domains and time domains. It is assumed that a PDCCH the destination of which is a mobile station is the PDCCH j. In this case, the mobile station receives the PDCCH j the destination of which is the mobile station, and receives data sent via the PDSCH j on the basis of the PDCCH j received.
A mobile station detects a PDCCH the destination of which is the mobile station, and receives downlink data. The mobile station then detects an error in the downlink data. If the mobile station does not detect an error in the downlink data, then the mobile station returns ACK (ACKnowledgement) to a radio base station. If the mobile station detects an error in the downlink data, then the mobile station sends NACK (Negative ACK) to the radio base station. If the radio base station receives the ACK, then the radio base station sends the next data. If the radio base station receives the NACK, then the radio base station resends the data sent previously.
FIG. 27 illustrates the sending of downlink data and a response thereto. In FIG. 27, downlink data which a radio base station sends to a mobile station and ACK or NACK which the mobile station sends to the radio base station are indicated.
As illustrated in FIG. 27, the radio base station sends downlink data to the mobile station. The mobile station detects an error in the downlink data received. If the mobile station does not detect an error in the downlink data received, then the mobile station sends ACK to the radio base station. On the other hand, if the mobile station detects an error in the downlink data received, then the mobile station sends NACK to the radio base station as illustrated in FIG. 27. In this case, as illustrated in FIG. 27, the radio base station resends the downlink data which the radio base station sent previously.
When the mobile station sends uplink data, the radio base station sends UL allocation grant used for sending the uplink data to the mobile station which sends the uplink data via a PDCCH. The mobile station uses a radio resource designated by the radio base station for sending the uplink data. There is a case where ACK or NACK as a response to the sending of downlink data is to be sent. In such a case, the mobile station multiplexes the ACK or NACK and the uplink data and sends the ACK and NACK by the use of part of the radio resource assigned for sending the uplink data.
FIG. 28 illustrates UL allocation grant and uplink data sent on the basis thereof. FIG. 28 illustrates UL allocation grant which a radio base station sends to a mobile station and uplink data which the mobile station sends to the radio base station.
The radio base station sends the UL allocation grant indicated in FIG. 28 to the mobile station via a PDCCH. The mobile station sends the uplink data on the basis of the UL allocation grant sent from the radio base station.
A method for sending ACK or NACK information as a response to the sending of downlink data depends on whether the mobile station sends uplink data. That is to say, there are two methods for sending ACK or NACK information as a response to the sending of downlink data. The case where the mobile station does not send uplink data will be described first.
FIG. 29 is a view for describing a method for sending ACK or NACK in the case of uplink data not being sent. FIG. 29 illustrates a PUCCH (Physical Uplink Control Channel) sent from the mobile station to the radio base station. If the mobile station does not send uplink data, then the mobile station sends ACK or NACK via a PUCCH which is assigned thereto in advance (or which is associated with a radio resource via which the downlink data is sent). In FIG. 29, the frequencies of PUCCHi and PUCCHj change by the slot (0.5 ms). The reason for this is to obtain a frequency diversity effect.
The case where the mobile station sends uplink data will be described next.
FIG. 30 is a view for describing a method for sending ACK or NACK in the case of uplink data being sent. FIG. 30 illustrates a PUSCH (Physical Uplink Shared Channel) assigned by a PDCCH (UL allocation grant sent via a PDCCH).
As illustrated in FIG. 30, if a PUSCH is assigned, then the mobile station time-multiplexes the uplink data and the ACK or NACK and sends them to the radio base station (see, for example, R1-073128, “HARQ symbol to RE mapping”, 3GPP TSG RAN WG1 Meeting #49bis, Orlando, Fla., USA, Jun. 25-29, 2007).
With the above ACK or NACK sending method, however, an uplink data format which the radio base station expects does not match the format of uplink data which is actually sent by the mobile station. As a result, the radio base station may be unable to receive the uplink data properly.
FIG. 31 is a view for describing a format mismatch (part 1). FIG. 31 illustrates downlink scheduling information 301, UL allocation grant 302, and downlink data 303 sent from a radio base station to a mobile station, and uplink data 304 sent from the mobile station to the radio base station. Forward error correction coding has been performed separately on the downlink scheduling information 301 and the UL allocation grant 302.
In FIG. 31, it is assumed that the mobile station fails to detect the downlink scheduling information 301 and that the mobile station succeeds in detecting the UL allocation grant 302. In this case, the mobile station fails to detect the downlink scheduling information 301, so the mobile station does not perform the process of receiving the downlink data 303. On the other hand, the mobile station succeeds in detecting the UL allocation grant 302, so the mobile station sends the uplink data 304 to the radio base station as illustrated in FIG. 31.
The mobile station does not perform the process of receiving the downlink data 303, so the mobile station does not perform error detection on the downlink data 303. Therefore, as illustrated in FIG. 31, the mobile station does not multiplex the uplink data 304 and ACK or NACK and sends only the uplink data 304 to the radio base station.
FIG. 32 is a view for describing a format mismatch (part 2). Elements in FIG. 32 that are the same as those illustrated in FIG. 31 are marked with the same symbols and descriptions of them will be omitted.
In FIG. 32, it is assumed that the mobile station succeeds in detecting downlink scheduling information 301 and UL allocation grant 302. In this case, the mobile station receives downlink data 303, so the mobile station performs error detection on the downlink data 303, multiplexes uplink data 304 and ACK or NACK 305, and sends them to the radio base station.
In the case of FIG. 31, only the uplink data 304 is sent. In the case of FIG. 32, the uplink data 304 and the ACK or NACK 305 are multiplexed and are sent. If uplink data and ACK or NACK are multiplexed and are sent to the radio base station, then a PUSCH transmission format which the radio base station expects does not match a PUSCH transmission format which the mobile station actually uses for sending.
That is to say, when the radio base station sends downlink data, the mobile station may fail to detect downlink scheduling information and succeed in detecting UL allocation grant. In this case, though the mobile station needs to multiplex uplink data and ACK or NACK and send them, the mobile station sends only the uplink data. As a result, the radio base station may not be able to receive the uplink data correctly.